Photographic sensitized papers excellent in fluorescent brightening effect and process for preparing the same

ABSTRACT

A PHOTOGRAPHIC SENSITIZED PAPER CAN BE GREATLY ENHANCED IN FLUORESCENT BRINGTNEING EFFECT BY INCORPORATING INTO A BINDER IN THE PHOTOGRAPHIC LAYER A STARCH DERIVATIVE HAVING IN COMBINATION A AMINOGULANIDINE GROUP AND AN ALKEHYDE GROUP. THIS STARCH DERIVATIVE IS A MORDANT WHICH MAKES THE BINDER COMPLETELY NON-DIFFUSIBLE TO A FLUORESCENT DYE.

United States Patent PHOTOGRAPHIC SENSITIZED PAPERS EXCEL- US. Cl.96--82 4 Claims ABSTRACT OF THE DISCLOSURE A photographic sensitizedpaper can be greatly enhanced in fluorescent brightening effect byincorporating into a binder in the photographic layer a starchderivative having in combination an aminoguanidine group and an aldehydegroup. This starch derivative is a mordant which makes the bindercompletely non-diifusible to a fluorescent dye.

This invention relates to photographic sensitized papers which areexcellent in fluorescent brightennig effect and to a process forpreparing the same. More particularly, the invention pertains to aphotographic sensitized paper which contains in the photographic layer,an aminoguanidized dialdehyde starch in a form bonded to an anionicfluorescent brightening agent, and to a process for preparing aphotographic sensitized paper which is excellent in fluorescentbrightening effect by incorporating into a binder forming thephotographic layer, an aminoguanidized dialdehyde starch either in aform previously bonded to an anionic fluorescent brightening agent or inthe form as it is so as to be bonded thereto within the photographiclayer.

H-eretofore, a process for enhancing the whiteness of textiles or papersby the use of a group of organic compounds called fluorescentbrightening agents or optical bleaching agents has been developed andhas come to be widely applied to photographic sensitized papers, and theuse of said process is common at present. However, in said process,there are several problems which have not sufficiently been solved yet.

The above-mentioned fluorescent brightening agents are organic compoundswhich absorb ultraviolet rays and emit blue to purple fluorescence, andwere developed to overcome such drawbacks that fibers employed for theproduction of papers and cloths, regardless of whether the fibers arenatural or synthetic, have a very slight yellowish color and are notsufiiciently white, in general. As such fluorescent brightening agents,there have chiefly been developed those of the anionic type whichpossess direct dyeability for many fibers such as cotton, silk, nylon,etc. Depending on the use, however, there are those which are differentin structure. Generally, the said agents adsorb on fibers and are notremoved by water-washing. Further, they are ordinarily direct dyes asmentioned above, and therefore they adsorb well on wood fibers forpapers and are markedly excellent in brightening effect on the papersthemselves. However, when they are applied to photographic sensitizedpapers which have been prepared by placing a baryta layer orphotographic layer on a paper base such as mentioned above, there aremany cases where the photographic sensitized papers are not alwayswhitened sufficiently. The reason therefore is that gelatine, which isthe main component of a binder used in the photographic layer or barytalayer, absorbs ultraviolet rays to a considerable extent and, moreover,does not have sufficient dyeability for any optical bleaching agentswhich are commercially available at present. In the case of a barytalayer, no problem occurs if a fluorescent brightening agent, which iswell adsorbed on barium sulfate particles, is used, since the amount ofbinder contained in said layer is very slight, and thus a brighteningeffect can be sufficiently achieved, in general, by the use of afluorescent brightening agent for paper. However, when an ordinaryphotographic emulsion layer or an over layer is coated thereon, theintensity of the ultraviolet rays reaching the base is weakened and thebrightening effect of the fluorescent brightening agent is greatlydisturbed, because the binder contained in said layer is composed mainlyof gelatine, which absorbs ultraviolet rays. This fact, coupled with thecolor of gelatine (yellowish brown), lowers the brightness and clarityof the white background of the printing paper. If several emulsionlayers and intermediary layers are laminated, as in the case of a colorpaper, the clarity of the background is further deteriorated, coupledwith coloration due to incorporated couplers and light-sensitive dyes.Such detrimental effects can be reduced to a certain extent by replacingpart or all of the gelatine with a synthetic resin having lesscoloration, such as polyvinyl alcohol. This, however, cannot be acomplete solution to the problem. It has therefore been absolutelynecessary to add suflicient amounts of fluorescent brightening agents tophotographic emulsion layers, intermediary layers and over layers.

Most of these water-soluble fluorescent brightening agents are anionicand are not injurious to the photographic emulsions themselves. However,sensitizing dyes, anti-fogging agents and similar additives for silverhalide emulsions are cationic, in general, and therefore the brighteningagents agglomerate by interaction with said additives and adverselyeffect the adsorption of said additives onto the silver halide particlesto bring about detrimental effects in general.

Accordingly, the fluorescent brightening agents, which are usable atpresent by addition to photographic emulsions, are not only greatlyrestricted in kind but also limited in the amount which is to be added,and hence they display sufficient brightening effects only withdifficulty. Moreover, in the acidic state, gelatine adsorbs anionic dyequite well, but in an alkaline state, it readily desorbs and liberatesthe dye, as is well known, so that a considerable portion of the dye islost during such photographic treatments as development, fixing andwater-washing. That is, the dye elutes in an alkaline developingsolution and, even though the adsorption amount again increases due tothe acidity of the fixing solution and the elution ceases, the escape offluorescent dye is inevitable if long term waterwashing is effected bythe use of water with a high pH. Moreover, in the water-washing of aprinting paper, another peculiar disadvantage occurs, which is not seenin the water-washing of a film. This disadvantage is that most of thefluorescent dyes are acidic direct dyes and hence adsorb well on thefibers of the paper rather than on the gelatine. Accordingly, the dyetends to gradually transfer from the emulsion layer to the base.Furthermore, in the case where printed paper pieces may have overlappedone another in water during the water-washing treatment and the waterhas not sufficiently been stirred, the fluorescent dye in the emulsionlayer of one sheet of paper is transferred and adsorbed, according tothe principle of imbibition, onto the paper bases of a different sheetof paper which was kept over-layed on it in the washing water.Consequently, the effect of water-Washing cannot be realized at all onthe surfaces of the printed paper facing the back of another sheet butrather the fluorescent dye is partly lost and causes a rapid decrease inbrightening effect. Thus, it is not the completeness or incompletenessof the water-washing but rather the skillfulness or lack of skill inperforming the water-washing treatment and the 3 superiority orinferiority of the equipment result in marked unevenness in thewhiteness of finished prints and thus great difficulties in thetreatment of large quantitles of small sheets of printed papers areusually brought about.

Further, the disadvantages and difliculties due to lnteraction of theaforesaid fluorescent brightening agents added to emulsions with suchemulsion additives as sensitizing dyes, anti-fogging agents, etc. areparticularly marked in the case where a plurality of layers of delicatelight-sensitive emulsions containing various kinds of sensitizing dyesand couplers are laminated, as in the case of color printing papers. Asa means to overcome the difficulties encountered in the above cases,there has been devised and practiced a process in which the fluorescentbrightening agents are added, not to the light-sensitive emulsionlayers, but to intermediary layers or over layers. However, the saiddyes not only easily diffuse and penetrate into the emulsion layers butalso readily diffuse and escape, during the photographic treatments,into the paper bases and treating liquids. Accordingly, in treating theprinting papers in the form of rolls, no substantial problem arises butin treating them in the form of sheets, there are brought about suchdisadvantages that unless much care is taken, the finished prints becomemarkedly uneven in whiteness and definite finishing can only bedifficultly attained; as in the case of the aforesaid black-whiteprints. In the case of black-white printing papers, therefore,fluorescent dyes are added in sufficient amounts to the paper bases andin small amounts to emulsion layers and over layers, in general. In thecase of color printing papers, however, fluorescent dyes are not added,in general, to the emulsion layers, intermediary layers and over layers,but the fluorescent brightening effects are displayed, in general, insuch a manner that prints which have been washed at the final step inthe course of developing and finishing treatment are immersed in aliquid containing a hardening agent such as formalin and a fluorescentbleaching agent, which is called a stabilizing bath, to a thoroughlysaturated state with a fluorescent dye, followed by immediate drying. Inthis case, the fluorescent dye in the liquid absorbed in the binderlayer remains as it is in the photographic layers even though the dyehas not been completely adsorbed on the binder, and therefore the aboveprocess is tentatively effective. However, the adsorption of afluorescent dye varies depending on such conditions as concentration andpH of the said liquid. Since the concentration gradually decreases inthe case Where large quantities of printed papers are treated, it isquite difficult to control the concentration to a definite value becausethe concentration cannot be visually observed. Accordingly, a techniqueof a high degree of skill becomes necessary in order to manage theconcentration so as not to bring about unevenness in whiteness offinished prints.

It is therefore the primary object of the present invention to providephotographic printing papers which are excellent in fluorescentbrightening effect by the use of high molecular weight compounds, whichcan be completely mixed with gelatine and like binders, can bechemically combined therewith and can form firm bonds with the anionicfluorescent dyes employed.

The present invention intends to accomplish the abovementioned object byovercoming at one time the series of disadvantages derived from such afundamental cause that fluorescent dyes do not completely adsorb onbinders. According to the prior art, it is a theoretically deducibleconclusion that in order to remove the above-mentioned fundamental causeand to completely adsorb or bond fluorescent dyes onto binders, theremay be adopted such procedures that the dyes are enhanced in directdyeability to make them completely non-diffusible in gelatine layers;the molecules of the dyes are incorporated with reactive groups to bondthem through direct chemical bonds to the molecules of gelatine and likebinders; or gelatine and like binders are modified so as to becompletely deposited on the dyes. In practice, however, the aboveprocedures en- 4 counter extraordinary difficulties in synthetictechnique and have not yet been successful.

As the result of various studies, the present inventors have beensuccessful in overcoming the abovementioned difficulties using existing,commercially available, fluorescent brightening agents. That is, theessence of the present invention resides in that high molecular weightcompounds, which can be completely mixed and chemically bonded togelatine and like binders and which can form firm bonds (chiefly complexbonds) with said anionic fluorescent dyes, are incorporated in suitableamounts into binders thereby making the binders non-diffusible to thedyes. Such an idea has never been attempted heretofore. In the abovecase, the high molecular Weight compounds may previously have beenbonded to the fluorescent dyes or may later be bonded and incorporatedtherewith by treatment with solutions of the fluorescent dyes. This is akind of mordanting, which is quite often effected in the case of dyesother than the fluorescent dyes. For example, in the case of transferpapers of the color print process called irnbibition or dye transfer,substances serving as mordants for acid dyes are generally mixed withbinders, and polyvinyl pyridines or various polymers containingvinylpyridines as copolymerization components have been known as suchmordants. These polymers surely form firm bonds with acid dyes and areeffective as mordants for ordinary dyes, but they are not applicable tofluorescent dyes. For example, polyvinyl pyridines are not homogeneouslymiscible with gelatine and hence are ordinarily mixed therewith afterforming them into quaternary salts. When formed into quaternary salts,polyvinyl pyridines bond firmly to fluorescent dyes to cause a so-calledquenching phenomenon and the fluorescent dyes are completely deprived oftheir fluorescence. Consequently, no brightening effect at all can beattained, and only a yellow color due to inherent absorption isdeveloped. In the case of polyvinyl pyridines which have not been formedinto quaternary salts, no complete quenching is brought about. However,said polymers greatly weaken the fluorescence of fluorescent dyes andhence are not suitable for this purpose.

Further, diphenyl biguanide, 1,1,3-triphenyl-guanidine,anhydro-biguanide, benzyl alcohol, and the condensate of dicyandiamidineand formalin are sometimes used for the purpose of firmly bonding directazo dyes to gelatine. Most of them, however, are low in molecular weightand have an insufficient aflinity for gelatine and like binders, andprecipitates formed by bonding the binders to the dyes not only have acertain extent of diffusibility but also lower the bonding strength ofgelatine and like binders themselves. Accordingly, they are effective asdyeing assistants for fibers but are not suitable as mordants forcolorants of photographic layers, particularly for fluorescent dyes.

In contrast thereto, in the present invention, the mordants themselvesare not only high in molecular weight and low in ditfusibility but alsocrosslink with the binders to firmly bond thereto through the aldehydegroups contained in the mordants, as will be described below.Accordingly, the mordants do not absolutely come out of the photographiclayers but act as a kind of hardening agent for the binders.

The object of the present invention can be accomplished by using, as akind of high molecular weight mordant capable of making binders ofphotographic layers completely non-diffusible in fluorescent dyes,starch derivatives containing aminoguanidine groups in combination withaldehyde groups which not only have no such detrimental actions such aslowering the bonding strength of binders or weakening the fluorescencebut also serve as a kind of hardening agent for enhancing the bondingstrength of the binders.

The above-mentioned aminoguanidine group-containing starch derivativesare obtained by reacting aminoguanidine with conventional dialdehydestarches formed by the oxidation of starch with periodic acid. Thesereactions may be diagrammatically shown in the following drawing:

CHzOH J L Eta) Ethel...

ctr-on I OH OH Aminoguanidation l (Aminoguanidlzed dialdehyde starch)All the reactions go to completion with difliculty but they can befreely controlled. It is therefore possible to synthesize variousaminoguanidized starches different in free aldehyde group content and inaminoguanidation degree.

Originally, dialdehyde starches have been developed in order to use themin admixture with pulps for papermaking so that the resulting papers canbe made high in water resistance. The aldehyde groups contained in saidstarches are partly converted into hydrazones by means of hydrazidecompounds or aminoguanidine compounds. The reason therefor is that bysaid treatment, the dialdehyde starches are made cationic so that theycan be readily adsorbed, in water, on wood fibers of pulps which ischarged anionic in water and can be used with high efficiency.

Aminoguanidized dialdehyde starches, which are commercially available atpresent, are high in content of aldehyde groups and are excellent ashardening agents for photographic layers, but are low in content ofguanidine groups, which serve as seats for the adsorption and bonding offluorescent dyes. Accordingly, said starches are not always said to beexcellent, though they are not unusable for the object of the presentinvention. It is rather preferable to use those which have beendecreased in degree of initial oxidation with periodic acid andincreased in amount of reacted aminoguanidine. Generally, however,starch derivatives high in content of guanidine groups have a tendencyto lower the Water resistance of gelatine and like binders. Accordingly,it is desirable to use starch derivatives which are considerably high infree aldehyde group content and which can overcome the above-mentionedtendency to be enhanced in hardening power. However, the extent of thesefactors varies depending on the kind and properties of binders and onthe kind and amounts of fluorescent bleaching agents to be introduced,and therefore no decisive conclusion can be made with respect thereto.Accordingly, it is necessary to use suitable starch derivatives inoptimum amounts from an economic viewpoint.

In the process of the present invention, the amount of the aminoguanizeddialdehyde starch to be incorporated into the binder is desirably up to50% of the amount of the binder.

Further, the starch derivatives in the present invention can beincorporated not only into the photographic layers but also into thebaryta layers thereby saving formalin.

aldehyde starch) (162)1+( )m The following examples illustrate theinvention.

EXAMPLE 1 To a dispersion of 250 g. of a commercially availabledialdehyde starch (Sumstar-l75 produced by Miles Co., U.S.A.; oxidationdegree about 75%) in 750 ml. of water there is added, under stirring, asolution of 25 g. of a commercially available aminoguanidine bicarbonatein 250 ml. of water which has been adjusted to pH 3 by addition of asmall amount of hydrochloric acid, and the mixture is reacted at below40 C. for 2 hours. After filtration and water-washing, the reactionmixture is washed with methanol and is dried at a low temperature toobtain a white powder containing about 3% of nitrogen and 13% of water.In view of the amount of nitrogen, the amount of the resultingaminoguanidized dialdehyde starch is only about 6% of the total aldehydegroup. However, said starch is favorably bonded to a fluorescent dye andhas no detrimental effect on the fluorescence of the dye. Further, thestarch is high in free aldehyde group content and hence is veryeffective as a hardening agent to make it possible to use no suchphotographically injurious hardening agent as formalin. As a result, theaminoguanidized dialdehyde starch is excellent not only for warm toneprinting paper but also for color printing paper.

EXAMPLE 2 A dispersion of g. of a commercially available starch(Sumstar-lSO produced by Miles Co.; oxidation degree about 50%) in 300ml. of water is slightly heated to a semi-solid. To this semi-solid isadded a solution of 45 g. of aminoguanidine hydrochloride in 450 ml. ofWater which has been adjusted to pH 2, and the mixture is reacted atroom tempertaure for 20 hours. After filtration and water-washing, thereaction mixture is Washed with methanol and is dried at below 40 C. toobtain, as a white powder, a starch oxide in which about one half of thetotal aldehyde group content has been aminoguanidized. The thus obtainedstarch oxide is considerably weaker in hardening power than the starchobtained in Example 1. However, it is markedly effective in bondingpower to a fluorescent dye and hence is particularly excellent foreffecting the object of the invention.

7 EXAMPLE 3 T o a dispersion of 30 g. of a specially made dialdehydestarch (oxidation degree 10%) in 100 ml. of water is added, understirring, a solution of 5 g. of a commercially available aminoguanidinebicarbonate in 50 ml. of Water which has been adjusted to pH 2.5 byaddition of a small amount of hydrochloric acid, and the mixture isreacted at about 50 C. for 3 hours. The reaction liquid is adjusted topH 7-7.5 by addition of a small amount of caustic soda, and is thenheated to 90 C. to form a 20% solution. This solution is low in bothoxidation degree and aminoguanidation degree but can be incorporated ina large amount into a binder. Accordingly, it is economicallyadvantageous to use this solution as a part of such an expensive binderas gelatine. Further, the solution has less coloration and hence isfavorable in brightening effect.

EXAMPLE 4 T 100 g. of the aminoguanidized dialdehyde starch there isadded a solution of got a commercially available fluorescent dye(Leucophol B produced by Ciba Co., Switzerland) in 1 l. of water. Afterstirring, the mixture is allowed to stand for more than hours at arelatively low temperature (about 10 C.), and is then suctioned,filtered, water-washed and dried to obtain a fluorescent granularsubstance which is pale yellow in color. A suitable application amountof the thus obtained substance is 10-20 times as great as the ordinarilyemployed amount of a fluorescent dye.

EXAMPLE 5 To 100 g. of the aminoguanidized dialdehyde starch obtained inExample 2 there is added a solution of g. of a commercially availablephotographic fluorescent dye (Tinopal B, PHOTO, produced by Geigy Co.,Switzerland) in 5 l. of water, and the mixture is treated in the samemanner as in Example 4 to obtain a pale yellow powder. This powder cansufficiently display a fluorescent brightening effect when used in 3-5times the amount of a fluorescent dye itself.

EXAMPLE 6 (A) A 5% gelatine solution incorporated with 0.01% ofLeucophol B, and (B) a 5% gelatine solution incorporated with 0.1% ofthe Leucophol B-dyed aminoguanidized dialdehyde starch obtained as inExample 4 are separately applied each in an amount of about 100' g./m.onto baryta papers and are then dried. The thus treated papers are cutinto small pieces and are washed with water, whereby both paper piecesemit strong fluorescence and no marked difference is seen between thetwo. 'However, when the paper pieces are immersed in alkaline water andare then washed with water, it is observed that the paper piece (A) isreduced in fluorescence. Further, when the two are removed from thewater, individually placed, while wet, on filter papers with theemulsion surfaces facing the filter papers, are squeezed and are peeledoff from the filter papers after 15 minutes, it is understood that thefilter paper surface which is contact with (A) emits strong fluorescencewhereas the filter paper surface which is contact with (B) emits nofluorescence. From this, it is substantiated that a part of thefluorescent dye in the paper piece (A) has diffused and transferred intothe filter paper whereas the fluorescent dye in the paper piece (B) hasbeen made substantially completely nonditfusible.

EXAMPLE 7 (A) A mixture comprising gelatine and 10% based on thegelatine of the aminoguanidized dialdehyde starch obtained in Example 1,and (B) a mixture comprising gelatine and 3% of formalin are separatelyapplied onto baryta papers, so that the solid content of each mixtureapplied becomes about 5 g./rn. and are then dried. The thus treatedbaryta papers are cut into small pieces, and

8 the paper pieces are immersed for 10 minutes in a 0.25% solution ofTinopal BOP and are then dried. Both of the two paper pieces aresubstantially the same in appearance, strongly emit fluorescence andseem to be pure white. The two kinds of paper pieces are washed withwater in separate vessels with much care so that the paper pieces do notoverlap each other. In a period of about 1 hour, it is not consideredthat any marked difference has occurred between the two. However, whenthe film surfaces of the paper pieces are closely contacted, while wet,with filter papers, like in the case of Example 6, are put betweenpolyethylene films or acetate bases so as not to dry, allowed to standfor a while and then taken up, it is found that the portions of filterpapers which have contacted with the two paper pieces (A) and (B), emitconsiderable fluorescence. This is not because the mordant employed in(A) is inferior but because in the film of (A), gelatine is present insubstantially the same amount as in (B), in addition to the fluorescentdye firmly adsorbed and bonded loosely onto the mordant, and saidgelatine has loosely adsorbed the fluorescent dye, as in the film of(B). When the films are repeatedly contacted, in the same manner asabove, with the surfaces of fresh filter papers wetted with water so asnot todry the films and are repeatedly allowed to stand, considerabletransfer of fluorescence is seen at the initial stage in both paperpieces (A) and (B). After a while, however, it is observed that (B) issubstantially completely deprived of fluorescence, whereas (A) stillretains strong fluorescence. According to the above process also, it ispossible to clearly substantiate the fact that mordant-dyed fluorescentbrightening agents are excellent in non-diffusibility.

EXAMPLE 8 To a high speed silver chlorobromide emulsion prepared from 1kg. of silver nitrate is added, together with other ingredients andadditives, 1.6 l. of a 5% solution of the bonded product of Leucophol Band aminoguanidized dialdehyde starch which has been obtained as inExample 4 and the total amount of the mixture is made about 50 kg. Thismixture is applied onto an ordinary, whitened baryta paper to form alayer. Onto this layer is applied, as an over layer, a mixturecomprising 10 kg. of a 1% gelatine solution and 200 l. of a 5% solutionof the bonded product obtained as in Example 4, whereby a pure whitesensitized paper favorable for enlargement is prepared. The merits ofthe dye employed in this example are that it has no detrimental effecton the emulsion and is not deteriorated in whiteness even when theprinted paper is subjected to a prolonged washing treatment.

EXAMPLE 9 In the case of a color paper of the multi-layered emulsiontype which is prepared according to a known manner, if each of theemulsion layers, intermediary layers and over layer is incorporated withabout 12 g. per liter of the coating liquid therefor of the product ofExample 5, there is obtained a color paper which does not suffer fromvariation in fluorescent brightening effect during the treatment thereofand which is not particularly required to be treated with a brighteningdye solution in a stabilizing bath. It is, of course, possible tofurther increase the whiteness of the paper by subjecting same,immediately before the final ferrodrying treatment of the paper, as inthe case of an ordinary color paper. In this case, said treatment is notuseless but the brightening efiect attained by said treatment is notgreat and the consumption of fluorescent dye in the bath is not much.Accordingly, there are such advantages that the bath may be low in dyeconcentration and is easily operated and managed for a long period oftime, and less unevenness is seen in finishing. Thus, the color paperprepared according to the above process is far more easily subject tohandling than a common color paper.

9 EXAMPLE 10- In a color paper of the multi-layered emulsion type whichis prepared according to a known process, a fluorescent brighteningagent, which tends to give detrimental effects to the photographicproperties thereof, is not used at all and, in place thereof, only anamino-guanidized dialdehyde starch, which becomes a mordant therefor, isadded to each of the emulsion layers, intermediary layers and over layerin an amount of about 1-5 g. per liter of the coating liquid therefor.The amount of said starch to be added is increased or decreaseddepending on the concentration of binder in each layer, or on thepresence or absence and kind of coupler, and the degree of hardening andswelling properties of each layer is so controlled as to become definitewithout adding other hardening agent, e.g. formalin or a compoundyielding formalin by decomposition which later gives deterrnentaleffects to color dyes or couplers. In this case, the aminoguanidizeddialdehyde starch acts, in the raw printing paper, only as a hardeningagent, and the function thereof as a mordant is latent until thetreatment has been complete. Accordingly, the color paper of thisexample may be treated, after the developing treatment and immediatelybefore the drying treatment, by immersing the paper in a socalledstabilizing bath containing a suflicient amount of a fluorescentbrightening dye, as in the case of a common color paper. The operationand control required therefor should be slightly more accurate than thecase of Example 9. Unlike in the case of a conventional paper, however,the fluorescent dye in an amount exactly proportional to the amount ofthe aminoguanidized dialdehyde starch added is firmly adsorbed on thepaper, so that the consumption of the fluorescent dye is exactlyproportional only to the surface area of the paper under treatment,substantially regardless of the concentration of the bath. Accordingly,the replenishment of the dye is simple, and an 10 excellent brighteningeffect less varied and free from unevenness can be easily attained.Moreover, the raw printing paper contains neither an injuriousfluorescent dye nor formalin and hence is favorable in storability.Thus, there are attained added advantages.

What is claimed is:

1. In a photographic sensitized paper containing a fluorescentbrightening agent, an improvement wherein the fluorescent brighteningagent is bonded to an aminoguanidized dialdehyde starch.

2. In a process for preparing photographic sensitized papers with afluorescent brightening effect, an improvement wherein an anionicfluorescent brightening agent is bonded to an aminoguanidized dialdehydestarch either before being incorporated into a binder forming thephotographic layer, or after said agent and aminoguanidized starch isincorporated in said binding layer.

3. A photographic sensitized paper according to claim 1, wherein theaminoguanidized dialdehyde starch is also contained in the baryta layer,in addition to the photographic layer.

4. A process according to claim 3, wherein the aminoguanidizeddialdehyde starch is incorporated into the binder in an amount of up tobased on the amount of the binder.

References Cited UNITED STATES PATENTS 2,882,156 /1959 Minsk 9684 NORMANG. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl.X.R.

